Wireless Sensor Networks (WSNs) include a plurality of spatially distributed sensor nodes that monitor physical conditions in a real world environment, and are used in environment and habitat monitoring, traffic control, home automation and stock tracking. Most current solutions that utilize sensors are vertical in their implementation. The operator is used as a bit pipe, and each WSN implementation uses its own protocols. As in the case of classical networks, applications that use data collected by sensor nodes in the WSN have their “channel” towards the sensor nodes. Each application is tailor-made containing specialized and in most instances proprietary components. Furthermore, there is no cross utilisation of data and sensors between different services. This situation leads to high development costs and relatively high costs for implementations and operating. Typical examples of such applications are industrial applications such as fleet management and logistics.
The integration of a WSN with a telecommunication network offers a network environment convenient for new and appealing WSN based services, for example smart home appliances, services for disabled and elderly people and so on. Furthermore, such integration may allow more flexible and efficient use of collected data. Data collected from sensor nodes comprising a WSN can be made available to a communications network via a WSN gateway.
Horizontal solutions offer a layered system design, based on the reuse of common functions and services in a distributed (networked) system. Different layers include clients (e.g., users, applications), middleware control functions, and sensor networks. Such an approach offers a clear separation between layers and hides WSN specifics from clients. Middleware functions provide a mapping between client requests and available WSNs.
Location based services (LBS) refer to a family of services that are based on utilizing information regarding the location of resources. Resources include anything that can be monitored, such as an object, person or animal. Location acquiring can be network or device based. In device-based positioning, using for example Global Positioning System (GPS), all position calculation is performed locally at the device (or resource). In order to use a location aware application, the locally calculated position has to be transmitted to the application, to make the application aware of the location of the resource.
LBSs in WSNs are mainly network-based. While device-based positioning guarantees privacy and full control of the locally calculated position disclosure, a problem with network-based positioning is that the positioned resource (which may be, for example, an end user in a communications network) is not in full control of its position data, thus creating concerns regarding privacy. For WSN monitoring, tracking, and resource controlling applications, strict security and privacy requirements may be imposed by the owners of resource tracking tags.
With regards to resource tracking, when a tracked resource moves from one WSN cover area to another, this may be referred to as roaming or handover. Sensor data for the roaming tracked resource must be acquired in a scalable way. An existing solution to track resources includes using a Session Initiation Protocol (SIP) subscription event framework and principles as defined by the IETF. In this case a central monitoring node sends an initial subscription (SIP SUBSCRIBE) for location information to each covered WSN. Each WSN accepts this subscription and is able to seamlessly notify (using the SIP NOTIFY message) the central monitoring node when a resource enters its cover area. A problem with this solution is scalability. If m is the number of active tracked resources and n is the number of WSNs, then this solution require m x n active subscription sessions with the central monitoring node, as IETF standards require that a SIP NOTIFY cannot be sent unless there is an active session.
An alternative solution, also based on the use of IETF standards, is to improve the usage of the SIP publication framework. Each WSN sends a SIP PUBLISH message to the central monitoring node with a list of resources for which the WSN has location information. When handover is detected, a WSN sends an updated PUBLISH message to the central monitoring node. In this case, the central monitoring node would know which WSN has the location information for a particular resource, and so does not need to broadcast a subscription to all WSNs. A problem with this approach is that there may be many resources whose location can be determined by a WSN, but are not of interest to the central monitoring node. With resources frequently moving from one WSN cover area to another, there is redundant signalling traffic as each WSN publishes changes to the central monitoring node even if there is no location aware application that is interested in signalled resource location information.
There are therefore issues with maintaining privacy and monitoring roaming tracked resources in a way that optimized network traffic.